Researchers at the University of Oxford have found that the risk of a rare type of blood clot is generally low but higher for people infected with Covid-19 than among people who have had the three vaccines approved in the UK – those made by AstraZeneca. , Modern and Pfizer.
The study, which was made available in advance on the Oxford website on Thursday before being published in a scientific journal, says the risk of cerebral venous thrombosis or CVT – also known as cerebral venous sinus thrombosis or CVST – is after Covid-19 infection. about “100 times larger than normal and several times higher than it is after vaccination or after flu,” in all age groups.
“Covid-19 significantly increases the risk of CVT, and adds to the list of blood clotting problems that cause this infection,” said Paul Harrison, professor of psychiatry and head of the Translational Neurobiology Group at the University of Oxford.
The University of Oxford, which developed the AstraZeneca vaccine, said the research came from a separate section of the university and was not linked to the vaccine team. The data used were obtained from external sources, specifically the European Medicines Agency.
Compared to the risk of blood clots from the three vaccines, the risk of infection is ‘8-10 times higher, and compared to the base, about 100 times higher for infection’, Oxford said in a news release. According to the research, the risk of CVT due to Covid-19 infection is about 10 times greater compared to the mRNA vaccines – Pfizer and Moderna. Compared to AstraZeneca, the risk of a Covid-19 CVT is approximately eight times greater. The Johnson & Johnson Covid-19 vaccine was not included in the analysis.
Using an electronic health record network of more than 500,000 positive cases of Covid-19, 489,871 cases vaccinated and 172,724 cases of influenza, the study found that 30% of cases of CVT occurred in the age group younger than 30 years , the greatest risk for blood clots.
‘Taking into account the balance between risks and COVID-19 risks, it is higher than in current vaccines, even for those under 30; something that needs to be taken into account when considering the balance between risks and benefits for vaccination, ”Harrison added.
Dr Maxime Taquet of Oxford’s Translational Neurobiology Group and a co-author of the study warned that data was still building up. Researchers also have yet to determine whether Covid-19 and vaccines lead to CVT in the same way, she said.
Experts have noted that CVT is so scarce, that even before the pandemic, there is limited data, and that the data and data sources surrounding the Covid-19 vaccines are inconsistent and limited.
‘Overall, the most important finding is that these CVT events are very rare – a few out of every million involved – in Covid-19 patients and in people who have had one of the vaccinations – but it was much rarer in humans. who had a vaccine. than in people who had Covid-19, ”said Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, in a comment to the Science Media Center in the United Kingdom. “The researchers do not claim that vaccines do not increase the risk at all, compared to the risk in people who have not been vaccinated and have not had Covid-19 – but they say the CVT risk in people who have had Covid-19 about 100 times the risk in the general population. ”
Some backgrounds: European and British drug regulators last week announced a “possible link” between the AstraZeneca vaccine and rare cases of blood clots, and the UK announced it would offer people under 30 an alternative vaccine. Other countries have followed suit and only offer people who are older than a certain age, or are like Denmark and Norway, who remove the vaccine completely. While advising the public to look at the signs of blood clots, regulators say the benefits of the shot are still worth the risk. The AstraZeneca vaccine is not approved for use in the United States.
Six reports of similar coagulation events after vaccination with the single-dose Johnson & Johnson vaccine prompted the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration to recommend the administration of the vaccine to allow further investigation.
Six women between the ages of 18 and 48 developed a cerebral venous sinus thrombosis, a blood clot in the area of the brain that collects and drains oxygen-depleted blood. Blood thinner, the typical treatment for blood clots, should not be used in such cases. The six reported cases included more than 6.8 million doses of Johnson & Johnson vaccine administered in the United States.
The EU, which relies heavily on the J&J vaccine to bolster its vaccination backlog, has also suspended use of the shot. The European Medicines Agency is expected to announce a decision next week on the administration of the Johnson & Johnson vaccine.
The WHO said on Thursday that “for the time being, the risk of blood clots is much higher for someone with COVID-19 than for someone who has taken the AstraZeneca vaccine.” Hans Kluge, WHO Regional Director, reiterates his recommendation of the AstraZeneca vaccine for all eligible adults and calls it ‘effective in reducing COVID-19 hospitalization and preventing deaths.’